Relationship to Alzheimer's disease and its related dementias This application is a response to NOT-AG-18-039 . This pilot study, using 60 subjects from one clinic, will be the first to test Alzheimer's disease (AD) patients directly on a thorough battery of standard, objective diagnostic tests of the vestibular system (ENG). Subjects will be patients with mild to moderate AD. We will estimate the prevalence of vestibular disorders in AD and compare their performance to that of healthy controls in the parent study who will have been tested on the same test battery. Therefore, we will be able to determine if the prevalence differs from age-matched controls. We will use clinical data to determine if severity of cognitive impairment or reduced hippocampal volume on MRI are related to increased prevalence of vestibular impairment.